The processing of particulate materials into solid bodies is a known technique, described, for example, in the following patent specifications: U.S. Pat. Nos. 4,113,480, 4,305,756, 4,544,694, 4,661,315, 4,765,950, 5,006,164, 5,122,326, 5,240,513 and 5,337,531, European patent nos. 0324122 and 0409646, and Japanese patent application nos. 59-121150 and 365552. Metal powders are compounded with a binder system and shaped by injection moulding. The binder is then removed from the moulded green body prior to sintering into a solid component. The binder systems that are used in the prior art are progressively softenable and are removed using heat or partial dissolution in solvents with subsequent heating. These methods are always associated with the use of a thermoplastic polymer, having a thermoplastic behaviour throughout the heating cycle. The thermoplastic polymer becomes quite soft during the initial heating cycle which is initiated to remove wax based binder components through melting, and increases in softness as the temperature increases. As a result of this increasing softness the polymer reaches a stage where it cannot support the metal or powder effectively to retain the shape of the part, thus causing distortion, deformation defects in the parts. This also limits the shapes of the parts that can be processed using processes of the prior art. Furthermore this also limits the type, size or shapes of metal powders that can be used in the processes of the prior art. In order to reduce the effect of softening of a thermoplastic polymer binder, the use of fine powders, typically less than 10 .mu.m in size, and irregular shape have been suggested. It may also be necessary to prolong the heating cycle, often to uneconomical lengths. Both these have a serious impact on the quality, economy, usage of material and the size of the processable parts. Furthermore the decomposition of the binder as it moves through an increasingly soft phase can leave residual products that contaminate the metal or ceramic particulate material. Processes of the prior art also require the shape of the powder particles to be partially irregular or irregular when larger particle size (up to 10 .mu.m) powders are used, but spherical or near spherical when smaller sized powders are used. This is in order to take advantage of some packing of the particles due to interlocking of irregular shapes, or the high surface energy of fine spherical particles, to bond the particles together. This unquantifiable packing and energy behaviour lead to unpredictable deviations of the final product properties.
Accordingly, there is a need for an improved binder composition for use in forming solid bodies from particulate materials.
Furthermore in prior art processes binder compositions for metals differ from binder compositions for ceramics. There is therefore a need for a binder composition that can be used for processing metal and ceramic powders.